The goal of this project is to determine the role of neutrophils, proteases and immunologic mediators in damaging the lung and exacerbating infection in the chronic lung disease of cystic fibrosis. This information is obtained by systematic examination of inflammatory cells and epithelial lining fluid obtained from bronchoalveolar lavage of well characterized cystic fibrosis patients. The study population includes those with mold and moderate disease, as well as those participating in therapeutic trials. Prior studies in stable, clinically mild patients suggested the presence of ongoing infection and inflammation. Comparisons of cystic fibrosis patients and healthy subjects found elevated levels of immune mediators such as leukotriene B4 in the epithelial lining fluid, suggesting that this mediator may play a role in recruiting neutrophils to the airways and stimulating them to release their injurious products. Persistent neutrophil influx, which characterizes the inflammatory response to persistent infection in this disorder, contributes to lung damage by a variety of mechanisms.